A coalition is a pact or treaty among individuals or groups, during which they cooperate in joint action, each in their own self-interest, joining forces together for a common cause. This alliance may be temporary or a matter of convenience. A coalition thus differs from a more formal covenant. Possibly described as a joining of 'factions', usually those with overlapping interests rather than opposing.

In international relations, a coalition can be an ad hoc grouping of nations united for a specific purpose. Sometimes, such groups are diverse and are characterized by some degree of commonalities. Sometimes, the degree of uncommonalities would lead some to perceive the group's bond as being ordinarily unlikely; here it can indicate the fact the historical ties may no longer be in operation, and the coalition members, instead, are joined by a new intention, not necessarily prior bonds.

A coalition might also refer to a group of citizens uniting behind a common goal. Many of these are grassroots organizations, like the Christian Coalition.

It can also be a collaborative, means-oriented arrangement, especially a temporary one, that allows distinct people or organizational entities to pool resources and combine efforts in order to effect change. The combination of such persons or entities into one body, as a union, variously organized and structured, but generally less formal than a covenant. Although persons and groups form coalitions for many and varied reasons, the most common purpose is to combat a common threat or to take advantage of a certain opportunity; hence, the often-temporary nature of coalitions. The common threat or existence of opportunity is what gives rise to the coalition and allows it to exist. Such collaborative processes can gain political influence and potentially initiate social movements. According to Sidney Tarrow, four elements are necessary to maintain a coalition:

Members must frame the issue that brings them together with a common interest.

Members’ trust in each other and believe that their peers have a credible commitment to the common issue(s) and/or goal(s).

The coalition must have a mechanism(s) to manage differences in language, orientation, tactics, culture, ideology, etc. between and among the collective's members (especially in transnational coalitions).

The shared incentive to participate and, consequently, benefit.

Coalitions manifest in a variety of forms, types and terms of duration:

Campaign coalitions with high intensity and long-term cooperation

Federations, characterized by relatively lower degree of involvement, intensity and participation, involving cooperation of long duration, but with members’ primary commitment remaining with their own entities

Event-based coalitions that have a high level of involvement and the potential for future collaboration.

Economics

A coalition in economics refers to a group of companies that create a mutual trust between each other in order for increased profit. For example, Dunkin' Donuts and Baskin-Robbins create a coalition by having shared stores and thus shared revenue.

Political science

Within political science, coalition theory is using game theory to analyze the formation, workings and break-up of coalitions. Coalitions also describe alliances between civil society organizations, such as labor unions, community organizations and religious institutions. Sometimes called labor-community coalitions, coalitions have proven to be an important strategy for social change in many contexts. Yet their power is variable, dependent on the context in which they are organizing and the strategies used by the organizers, as documented in the book Power in Coalition.[1]

Activism

Civil society, activist and nonprofit groups often call themselves "coalitions" when they join together. It can be temporary or long-term. Such coalitions are defined by the cause which unites the members groups, although sometimes there is also a geographical dimension, such as in the West Suburban Faith Based Peace Coalition, based in suburban Chicago. Most often coalitions of activists and advocates support each other when one faction takes the lead in a particular movement. Coalitions of activists work best once there is a mutual respect for the strengths of each organization/individual involved, and there is less overlap.

In some instances the organization consists of only one person. The often-cited Save the Plastic Bag Coalition, for example, lists only one person, Stephen Joseph, on the contact page of its website.